/Engine/Plugins/Editor/ObjectMixer/ObjectMixer/Source/ObjectMixer/Public/Views/List/ObjectMixerEditorList.h
Force returns result from Filter->ForceGetObjectClassesToPlace. Generally, you want to get this from the public performance cache.
[TSet](API\Runtime\Core\Containers\TSet)< [TSubclassOf](API\Runtime\CoreUObject\Templates\TSubclassOf)< [AActor](API\Runtime\Engine\GameFramework\AActor) > > ForceGetObjectClassesToPlace()